This invention relates generally to interfacing a station with a communications network. In a particular aspect of the preferred embodiment of the invention, a device operating in a master-slave mode of operation is adapted to a token ring network operating in a peer-to-peer mode.
An example of a communications network with which the present invention can be used is one which connects one or more musical instruments, computers and synthesizers so that the connected equipment can be used to create and play synthesized music. A specific implementation of such a network is a local area network that uses the token passing access method, whereby the network can be referred to as a token ring network.
A token is typically a series of bits in a predetermined unique format. In a token ring network, the token passes sequentially from station to station until a station seizes the token and transmits its own data. Other stations on the network "listen" to the transmitted data, utilize it if it is addressed to them, and pass the data on. When the transmission concludes, the seizing station relinquishes the token by transmitting the token format back onto the network. In such a network, data flows circularly from the current token-holder around the ring.
To enable network transmissions to be recognized, they need to conform to some standard. A well-known standard is the Synchronous Data Link Control (SDLC) protocol. SDLC is a bit-oriented synchronous protocol.
A device that works with this protocol is the Zilog 8530 serial communications controller. One of these devices can operate in an SDLC loop mode to interface a station to a network having a ring topology. The 8530 serial communications controller in SDLC loop mode is designed for use as part of a master-slave network, in which each message is either from the ring master to a slave or from a slave to the ring master. In this configuration, while a slave sends a message to a master, the master sends back all logic ones ("1") to the slave.
This master-slave arrangement, however, is not desirable for some applications. With regard to the music synthesis network mentioned above, peer-to-peer communications, wherein any station on the network can communicate directly with any other station without going through a master station, is preferred because of, for example, the greater flexibility of communication due to the direct station-to-station communication. In peer-to-peer communications, while one device is sending data, there is not another device on the ring sending it all ones. Instead, the data sent by that device goes all the way around the ring and back to the sender. Thus, the 8530 chip operating in SDLC loop mode has not been useful in peer-to-peer communications because it would not receive the expected stream of ones during transmission. Instead it would receive its transmitted data back so that it would likely transmit an improper format at the conclusion of its transmission.
One way to implement a peer-to-peer token ring network is to use an IBM Token Ring chip; however, this device is relatively expensive (e.g., about $35-$80) compared to the 8530 serial communications controller (e.g., about $3). Thus, it would be desirable to be able to connect a station to a peer-to-peer token ring network through an interface using the less expensive, but heretofore inapplicable master-slave device. This is accomplished by the present invention.